1. Field of the Invention
The present invention relates to a data transmission method and an apparatus therefor in a relay transmission type radio network.
2. Description of the Related Art
FIG. 18 is a diagram illustrating a cell configuration of a conventional cellular system. As for the cell configuration of this cellular system, it is comprised of cells 101 and base stations (nodes) 102, where a serviceable area is constituted by placing a plurality of cells as in FIG. 18. Each of nodes 102 is connected by a wire basic network 104 and a wire circuit 103, so that service signals such as voice and data and various control signals are communicated via these links. Moreover, there are cases where each of nodes 102 is connected to the wire basic network 104 by providing concentration stations or the like hierarchically between them. A terminal station 105 performs communication with the node 102, and transmits and receives various signals communicated by the wire basic network 104 and the wire circuit 103. The wire basic network 104 has a server apparatus installed for managing location information on the terminals and radio nodes, and performing accounting and so on.
In order to cope with the increase in the number of subscribers to the cellular systems such as portable telephones and the Fixed Wireless Access, a technique of reducing a cell radius to decrease a processing load per node is adopted. In the case of constructing the system with such minimal cells, a very large number of the nodes are placed so as to secure a service area.
In addition, in the case where a high density data transmission system such as multilevel modulation is applied in order to sup-linkport high-speed data transmission, the area covered by one node inevitably becomes smaller to secure required received quality, and so a very large number of the nodes are also placed in this case.
Furthermore, while the cellular systems were mainly designed in quasi-micro and microwave zones in the past, construction of the cellular systems using quasi-millimeter and millimeter wave zones is expected because of a crisis of frequency pressure. A higher frequency weakens a diffraction effect and makes it markedly straight so that an unexpected call becomes difficult, which inevitably leads to a smaller area covered by each node. To be more specific, a very large number of the nodes are also placed in such a case since a call area must be secured with the minimal cells.
In the case of constructing the systems with a large number of the minimal cells, it is essential to consolidate a wire network for the purpose of connecting the node group-link to the basic network. To connect a very large number of the geographically unevenly distributed nodes with the basic network, however, it is necessary to install the wire networks everywhere and so the cost of the entire system increases. Therefore, there is a technique of connecting the nodes by radio and performing relay transmission so as to expand the service area.
FIG. 19 is a diagram illustrating an example of the cell configuration wherein relay nodes 204, 205 and 206 are placed around a core node 203 connected to a wire network 201 by a wire circuit 202 and the relay nodes and the core node are connected by radio. A symbol 208 indicates an example of an area covered by the node. The up-link packet transmitted from a terminal 207 reaches the core node 203 via the relay nodes 205 and 204, and then the packet received by the core node 203 is communicated to the wire network 201 by way of the wire circuit 202. On the other hand, the down-link packet to the terminal 207 sent from the wire network 201 is sent to the core node 203 first by way of the wire circuit 202 and then is communicated from the core node 203 to the terminal 207 by way of the relay nodes 204 and 205.
In the case of transmitting the down-link packet in the cell configuration shown in FIG. 19, there was a challenge that the appropriate relay route must be selected out of a plurality of the relay routes according to the location of the terminal 207, and that, if the terminal station moves, the relay route of the down-link packet to the terminal station must be changed as appropriate following the move.